Production of fibers made of or containing polyvinyl alcohol



June 16, 1959' HIDENARI SUYAMA ETAL ,9

paonucnou OF FIBERS MADE OF 0R CONTAINING POLYVINYL ALCOHOL Filed Jan. 24, 1958 2 Sheets-Sheet 1 FIG. 3 v FIG. I

a so 3o E20 5 g o 3 IO f; 1: 70 v I00 v 300 500 I000 g Rlncflon Tim mini 3o Q O8 012 I0 l5 2O 25 30 Degree of Benzclizafion (moi N=QO5 2 mm mm Filed Jan. 24, 1958 June 1959 HIDENARI SUYAMA ETAL 2,390,927

PRODUCTION OF FIBERS MADE OF OR CONTAINING POLYVINYL ALCOHOL 2 Sheets-Sheet 2 Primary Hear Treormenr Partial Ac'eralizarion Dissolving in Wafer Spinning Srrerohing Secondary Heat Treorment Secondary Acetaiizafion Prodacr United States Patent PRODUCTION OF FIBERS MADE OF OR CON- TAINING POLYVINYL ALCOHOL Hidenari Suyama, Hiroshima-ken, Eiji Kobayashi, Rikita S'akata, and llkuzo Hata, Tokyo, Mitutaka Uzumaki and Masao Ishii, Hiroshima-ken, Takayuki Kiyota, Toyama-ken, and Hajime Haioka, Yamaguchi-ken, all of Japan, assignors to Mitsubishi Rayon Co. Ltd., Tokyo, Japan, a corporation of Japan Application January 24, 1958, Serial No. 711,055

13 Claims. (CI. 18-54) This invention relates to improvements in the production of fibers made of or containing polyvinyl alcohol. Fibers in the present specification includes not only fiber but also filaments.

Some defects of fibers made of polyvinyl alcohol or containing polyvinyl alcohol as their principal constituent include their liability to creasing, resistance to penetration by dyes and lack in wool-like handle as compared to "other synthetic fibers. These shortcomings hinder the development of polyvinyl alcohol fibers from being acceptable to the textile industry.

As a means for improving wool-like hand and low crease resistance, methods have recently been suggested that comprise improving the elastic properties of polyvinyl alcohol fibers in which the molecular structure is modified to resemble the molecular structures of wool .and cellulose acetate fibers. For example, methods have been introduced to treat heat-treated polyvinyl alcohol y-a'rn with nonylaldehyde or treat polyvinyl alcohol fibers with glyoxal. Such treatment has been recognized as improving the elastic properties of polyvinyl alcohol fibers to a certain degree. As a means of improving dyeability, proposed methods include acetalizing polyvinyl alcohol fibers with an aldehyde containing an amino group instead of nonsubstituted aldehyde, or chloroacetalizing polyvinyl alcohol fibers and then substituting chlorine with amino groups, or subjecting polyvinyl alcohol fibers to cyanoethylation treatment with acrylonitrile.

The above methods substantially relate to aftertreatment of polyvinyl alcohol products in the form of yarn or staple with the purpose of improving their wool-like hand, dyeability and crease resistance. Since the treatments were carried out in a heterogeneous system, it was not only ditficult to obtain uniform results, but also involved complicated procedures that offer a number of obstacles which prevent their application to commercial scale production.

The object of this invention is to provide an improved method for the production of polyvinyl alcohol fibers which are free from the above-mentioned disadvantages and is applicable to commercial scale production. We have found that remarkably improved wet heat resistance and elastic recovery at low strain can be imparted to polyvinyl alcohol fibers by heat-treating polyvinyl alcohol in solid form which contains not more than 0.2 11101 percent of unsaponified acetyl groups if necessary, to such a degree that polyvinyl alcohol becomes insoluble in cold water but soluble in hot water, partially acetalizing said heat-treated polyvinyl alcohol in a solid form with aldehyde or 'acetals thereof to such a degree that the product is still soluble in hot water, spinning said hot water soluble partially acetalized polyvinyl alcohol and subjecting the spun product to stretching, final heat-treatment and final acetalization. We have also found that polyvinyl alcohol fibers having exceptionally good dyeing properties are obtained in addition to the properties mentioned above when aldehydes containing basic groups or 2,890,927 Patented June 16, 1959 acetals thereof, such as amino acetaldehyde, dimethylamino acetaldehyde, piperidino 'acetalde'hyde or acetal thereof, are employed in the partial acetalization step of polyvinyl alcohol in solid form to such a degree that it still retains its hot water solubility. These fibers, however, even though possessing improved dyeing properties, have a tendency to discolor by the efiect of oxygen in the atmosphere when the fibers are exposed to high temperatures during the final heat-treatment process. We have further found that such discoloration is prevented by neutralizing the majority of combined acid that exists in polyvinyl alcohol which has been partially acetalized with aldehydes containing basic group or acetal thereof, with alkalies or by adding a color stabilizing agent, such as urea, formic acid, ammonium formate, formaldehyde, formaldehyde derivatives, formamide, dicyano diamide. Such color stabilizing agents are added 'to the spinning solution prepared from polyvinyl alcohol that has been partially acetalized with an aldehyde containing a basic group or acetal thereof. Furthermore, a combination of the above neutralization step and the addition of color stabilizers may also be employed.

'We have also found that in addition to the improvements in dyeability, wet heat resistance and elastic properties, further improvements in elastic properties can be achieved effectively by treatment with such aldehydes as 'benzaldehyde during the secondary acetalization stage. The conventional art of benzalization employs such expensive organic solvents, as methanol, acetic acid, acetone,

"and the treatment generally gives poor dyeability. The

present benzalization method has succeeded in the estabvinylalco'hol without sacrificing dyeability and wet heat resistance. When fibers obtained from polyvinyl alcohol partially acetalized with aldehydes or .acetals thereof are further treated with an aqueous benzaldehyde solution, preferably in the presence of formaldehyde, fibers having exceptional good wet heat resistance, dyeability and elastic properties are obtained.

In the drawings, Figure l is a graph showing the relationship between degree of acetalization versus reaction time. Figure 2 is a graph showing the relationship between color index versus amount of caustic soda. Figure 3 is a graph showing the relationship between dye absorption versus degree of benzalization. Figure 4 illustrates flow diagram of the most favorable embodiment for a method of preparing polyvinyl alcohol fibers according to the present invention.

Three principal and essential steps of the present invention will be discussed hereinafter.

1. Primary heat treatment-According to the present invention, polyvinyl alcohol in solid form is first subjected to a heat-treatment to the extent that it becomes insoluble in cold water but soluble in hot water. Such starting polyvinyl alcohol solids may be in the form of granules, fibers, films or chips. The primary heat-treatment of polyvinyl alcohol is carried out, while it is being pulverized, by heating the material in a kneader type apparatus at a temperature of 60 C. to C. for 10 hours to 30 minutes. When polyvinyl alcohol in fibrous, film or chip form is employed, the heat-treatment may be carried out by heating the material in either dry or wet state at a temperature of C. to 210 C. for 20 to one minutes. The heating media for dry heat-treatment may be air, inert gas or fused metal, and for wet heattreatment ammonium sulfate solution or steam. The heat-treated product is no longer soluble in cold water of room temperature or so but still soluble in hot water of 50 C. or higher. Fibrous polyvinyl alcohol for the above purpose is prepared by extruding an aqueous poly vinyl alcohol solution through spinnerettes having small openings into air or a coagulating bath. Polyvinyl alco,

hol films are prepared by extruding an aqueous polyvinyl alcohol solution through slits or by other suitable methods. Such films are made into chips by cutting the films into small pieces.

2. Partial qcetalizatin.--Polyvinyl alcohol in pulverized, fibrous, film or chip form is then treated with an aldehyde or acetal thereof to obtain the required partially acetalized product. Any of the aldehydes may be employed. However, in order to obtain improved dyeability, an aldehyde containing a basic group or acetal thereof is preferred. Examples of such aldehydes containing a basic group are selected from the group consisting of amino acetaldehyde, ethyl-amino, benzyl-amino acetaldehyde, dibenzyl amino acetaldehyde, dimethyl amino acetaldehyde, diethyl-amino acetaldehyde, pyrrolidino acetaldehyde, phthalimido acetaldehyde, piperidino acetaldehyde, dimethyl-amino propionaldehyde, dimethylamino benzaldehyde, dipropyl-amino acetaldehyde, bibutyl-amino acetaldehyde, diethyl-amino propionalde hyde, dipropyl-amino propionaldehyde, dibenzyl-amino 'propionaldehyde, piperidino propionaldehyde, dimethylamino butyraldehyde, diethyl-amino butyraldehyde, dipropyl-amino butyraldehyde, dibutyl-amino butyraldehyde, dibenzyl-amino butyraldehyde, piperidino-amino butyraldehyde and dimethyl-amino hydroxy butyraldehyde. Aldehyde having tert.-amino radical is effective for inhibition of discoloration during secondary heat treatment which will be referred to later.

Reactions between aldehydes or acetals thereof and polyvinyl alcohol are usually carried out in the presence of an acid catalyst. The acid catalyst may be an inorganic or an organic acid. Such acids, however, have a tendency to form an ester with polyvinyl alcohol. The esterification reaction between acids and polyvinyl alcohol occurs readily at high acid concentrations and/or at high reaction temperatures. When aldehydes exhibiting slow rates of reaction are employed, the possibility of ester formation is increased since higher acid concentrations and/ or higher temperatures are required to carry out the reaction. The formation of such esters is naturally undesirable since they will obstruct crystallization during the heat-treatment process. It is therefore important to employ a catalyst which possesses the least tendency to form an ester with polyvinyl alcohol when acetalization is carried out with aldehydes or acetals thereof exhibiting slow rates of reaction. For example, sulphuric acid shows a higher tendency to form an ester with polyvinyl alcohol than hydrochloric acid. Fibers obtained by known methods from partially dimethyl-amino acetalized polyvinyl alcohol in the presence of sulphuric acid catalyst shows a higher tendency to lose their dimensional stability as compared with fibers similarly obtained except that the partial acetalization reaction is carried out in the presence of hydrochloric acid catalyst.

The partial acetalization reaction must be terminated while the product still retains its solubility in hot water. The maximum degree of acetalization wherein hot water solubility is retained depends upon the type of aldehyde or acetal thereof. An example of the maximum degree of acetalization with several aldehydes is tabulated in Table 1.

TABLE 1 Maximum Type of Acetalization Degree of Acetalization, mol percent Formalization 15 Benzalization 7. 5 Aminoacetalization 11 3. Purification 0r washing.-The partially acetalized polyvinyl alcohol obtained in solid form is next subjected to a thorough washing treatment. The product is repeatedly washed with room temperature water ,until the waste solution shows a pH of 6.5 to 7.5. When polyvinyl alcohol is to be spun by a dry spinning process, the raw material must be highly pun'fied to remove all traces of impurities such as acids, alkalies and sodium acetate, otherwise the fiber product will tend to discolor during the secondary heat-treatment process. In the wet spinning process, purification of raw material is not required to the same extent since discoloration of the fiber during the secondary heat-treatment can be prevented to some extent by controlling the pH of the coagulation bath. However, in either case it is preferable to employ highly purified polyvinyl alcohol to prevent discoloration during the secondary heat-treatment process.

Acid catalysts, unreacted aldehydes and impurities in partially acetalized polyvinyl alcohol can be readily removed by washing with cold water. Since the product is in solid form,'the water can be readily removed by hydroextraction. This is an advantage of commercial importance which is achieved by retaining polyvinyl alcohol in solid form throughout the primary heat-treatment and partial acetalization processes in accordance with the present invention. The advantages over the homogeneous reaction system is self-evident since the homogeneous system gives poor washing efliciency even with employ,- ment of expensive organic solvents to purify the product after the reaction and also shows difficulties in obtaining suificient hydroextraction.

4. Spinning.Hot water is next added to the purified partially acetalized polyvinyl alcohol to form the spinning solution. The dissolution may be effected by the application of heat after addition of cold water. Untreated polyvinyl alcohol may be added, if required, during this dissolving stage. Kneaders, mixers or any other known type of dissolving apparatus may be used for dissolving the partially acetalized polyvinyl alcohol in water. The concentration of the spinning solution varies depending upon the method of spinning, but it is generally within the range from 10% to 40%. Common practice is to add a surface active agent during the dissolving stage. Fiber products may be obtained by the wet spinning or dry spinning method. The extruded fibers are next subjected to a stretching operation. Since the secondary transition temperature is approximately 82 C., stretching is generally carried out under heated conditions. Cold drawing may also be applied when Water which acts as a plasticizer is present in the fiber.

5. Secondary heat-treatment..When polyvinyl alcohol partially acetalized with an aldehyde or an acetal containing a basic group is employed as the raw material 'for spinning, the extruded fiber products will tend to discolor (yellow to brown) when exposed to heat during secondary heat-treatment process which will be described next, even when the material has been subjected to a thorough washing process as described above after the partial acetalization reaction. Discoloration begins to appear at temperatures between C. to C., and the degree of discoloration depends upon the basic group combined to the aldehyde or acetal thereof. This discoloration is believed to be due to combined acid radicals combining with the basic groups and forming salts. We have found that neutralization of the acid with an alkali is effective to prevent such discoloration. Examples of alkalies that have been found to be effective are strong bases such as sodium hydroxide and potassium hydroxide, and weak bases such as sodium carbonate and sodium acid carbonate. Two methods of neutralization are proposed. The first method comprises adding an alkali to the spinning solution. The second comprises immersing partially acetalized polyvinyl alcohol in solid form in an aqueous alkaline solution. The degree of neutralization of combined acid radicals with alkali is treatment.

determined by the following. experiment. A prepared from polyvinyl alcohol partially acetalizedas stataddition of alkali, and .passes through a minimum point after which the degree of discoloration further increases with increasing amounts of alkali. Each curve represents different nitrogen contents, and the higher the nitrogen content, the higher becomes the minimum degree of discoloration. This relationship is applicable to cases wherein partially acetalized polyvinyl alcohol immersed in an aqueous alkaline solution by determining the degree of discoloration with alkaline solutions of various concentrations.

It is seen from Figure 2 that the minimum value of discoloration obtained by alkaline neutralization increases with increasing basic groups in the polyvinyl alcohol molecule. This suggests that the heat stability of the existing basic groups themselves may also become the cause of discoloration. Various color stabilizers have been investigated, and we have found that organic reduction agents such as urea, formamide, formic acid, ammonium formate, formaldehyde, formaldehyde derivatives anddicyano diamide are most effective. However the homologs of these compoundsdo not always show the same color stabilizing effect. Application of these color stabilizers is similar to that of alkalies, and includes adding such agents to the spinning solution or immersing polyvinyl alcohol in aqueous solutions of such agents. In order to obtain the best results, it is preferable to add .not less than 2% to 5% (based on the weight of partially acetalized polyvinyl alcohol) of the above color stabilizing agents. Discoloration mentioned above is the discoloration that appears when polyvinyl alcohol fiber products are exposed to hot air during secondary heat- After the stretching operation, the fibers are subjected to a secondary heat-treatment process. A temperature of above 200 C. is adopted when the fibers are subjected to the treatment in dry state, whereas a temperature from 100 C. to 150 C. is applied when fibers are treated in wet state. Examples of the heating medium are air, inert gas, fused metal, aqueous solutions of ammonium sulfate and steam.

6. Secondary acetalization.Heat-treatments at relatively low temperatures such as wet heat-treatment or heat-treatment in the absence of air (for example in an inert gas atmosphere) are effective for the prevention of discoloration. Furthermore, fibers possessing sufficiently high wet and dry heat resistance may also be obtained without heat-treatment by forming cross-linkages within the fiber structure. A secondary acetalization treatment follows the secondary heat-treatment process. This is carried out under acidic conditions, but an antiswelling agent such as sodium sulfate, ammonium sulfate or dibasic sodium ortho-phosfate is added to the reaction bath in order to prevent swelling and shrinkage of the fibers during the acetalization reaction.

Fibers of improved elastic recovery at low strain are obtained from partially acetalized polyvinyl alcohol as described above, but further improvements in elastic properties can be obtained with such aldehydes as benzaldehyde, when the fibers are treated with such aldehydes during the secondary acetalization stage. However fibers thus treated generally become hydrophobic and exhibit poor dyeability. Therefore special dyeing processes such as the use of swelling agents become necessary.

The present fibers possess good dyeability and elastic properties. In the prior art, the benzalization reaction is carried out in the presence of expensive organic sol vents. We have found a method of commercial advantage wherein benzalization can be carried out in the presence of water. Since approximately 0.3% of benzassess? aldehyde dissolves in water at 20]C., the fibers are treated in this saturated benzaldehyde solution inj the presence of an acid catalyst. The acid catalyst maybe sulphuric acid or hydrochloricacid.

Formaldehyde may be added to the reaction bath if necessary. The addition of formaldehyde yields fibers of further improved wet and dry heat resistance compared to those treated with benzaldehyde alone. Furthermore effects upon the dyeability and elastic properties of the fibers can be controlled by controlling the respective amounts of formaldehyde and benzaldehyde that react with polyvinyl alcohol. The relationship between dye absorption and degree of benzalization is plotted in Figure 3. Partially dimethylamino acetalized polyvinyl alcohol was used as the basic .raw material in this experiment. Benzalization was carried outin the presence of formaldehye. If the degree of benzalization is low, a high degree of formalization is obtained and vice versa. As seen from Figure 3, dye absorptivity is good at low degrees of benzalization whereas at higher degrees of benzalization, dye absorptivity becomesrpoor. On the other hand, high dye absorptivity is maintained at high degrees of benzalization if the nitrogen content in the fiber is high. Thus the coexistence of formaldehyde in the benzalization bath has the advantage of yielding fibers that possess good elastic properties and wet and dry heat resistance without lowering their dyeability.

Fibers thus obtained exhibit excellent elastic properties and dyeability. The affinity of disperseddyestutfs to the fibers is increased when partially acetalized polyvinyl alcohol is employed as the starting raw material for spinning. When partial acetalization is carried out with aldehydes or acetals thereof containing basic groups, fibers made from such resins exhibit unexpected good dyeability not only with dispersed dyestuffs but also with acid dyestuffs. l r t it Advantages of the present invention can more fully be understood from the following statements which are explained comparing with the conventional processes. It is generally known that polyvinyl alcohol is highly reactive and it is easy to cause it to react with various aldehydes in the presence of acid catalysts to form corresponding polyvinyl acetals. Al'dehydes capable of reacting with polyvinyl alcohol include saturated and unsaturated aliphatic aldehydes, aromatic aldehydes, alicyclic aldehydes, heterocyclic aldehydes, amino-substituted aldehydes, halogen-substituted aldehydes, nitro-substituted aldehydes, hydroxyl-substituted aldehydes and alkoxy-substituted aldehydes.

Known processes up to the present date concerning the methods of reacting such aldehydes with polyvinyl a1- cohol are as follows: i

(1) A method of acetalization with an aqueous polyvinyl alcohol solution (homogeneous system).

(2) A method of acetalization which comprises first carrying out the reaction in a suspension of polyvinyl alcohol and converting the suspension to a solution as the reaction proceeds (homogeneous system).

(3) A method of acetalization which comprises carrying out the reaction simultaneously with the saponification of polyvinyl acetate (direct method).

(4) A method of acetalization in which polyvinyl alcohol reacts with aldehydes in a vapor phase.

The above known methods in the preceding paragraph relate to the acetalization of polyvinyl alcohol. There is no reference with regard to forming fiber products and evaluating the properties thereof from such acetals, except Lee et al.s report (J. Chem. Soc. (Japan), I-nc. Chem. Sec., 44, 46 (1941)) which describes thatformation of fibers by dry spinning polyvinyl acetals dissolved in an organic solvent, and also discloses that the fibers thus obtained possess a very low softening point and that their properties are not suitable for practical applications Itis common practice to combine heat-treatment and acetalization to improve the dry and wet heat resistance of polyvinyl alcohol synthetic fibers. .With regard to the heat-treatment process, I. Sakurada et al. have found a reduction in the lattice distance corresponding to A by X-i'ay diffraction patterns, and have confirmed an increase inthe degree of crystallization by means of the Geiger-Mueller counter. (I. Sakurada, K. Fuchino, Scientific Paper Inst. Phys. and Chem. Research, 21, 1077 (1942); I; Sakurada, Y. Nukushina, N. Mori, Chem. High Polymers (Japan), 12, 302, (1955).) In the manufacture of polyvinyl alcohol synthetic fibers, it is therefore necessary to enhance crystallization of the fiber structure during the heat-treatment process and also avoid conditions that will inhibit crystallization, in order to prevent decrease in resistance to dry and wet heat. Many of the investigations concerning improvements in the dyeability and elastic properties of polyvinyl alcohol synthetic fibers are mainly in the field of aftertreatment, that is, chemical treatment of extruded filaments or fibers. This is due to the recognition of the fact that the effect of heat-treatment upon the fibers is attributed to crystallization. The reason why little progress has been 'made inrthe field of copolymerization, which is consideredto 'be one of the first basic steps in the studies for improving the. properties of raw material to modify the properties of the fiber products, is due to the fact that polyvinyl alcohol synthetic fibers possessing sufficient resistance to dry and wet heat cannot be obtained since such copolymers greatly obstruct crystallization during the heat-treatment process.

According to H. Mark (Textile Research J., 23, 294 (1953)), it has been suggested that copolymerization may be classified into the following three general types:

where A and B are monomer units. (1) represents the conventional model of a copolymer molecule. No extensive studies ,to date have been made concerning the molecular models represented (II) and (III).

According to extensive studies on the improvement of properties of polyvinyl alcohol synthetic fibers, we have .found a commercial method for the manufacture of copolymers corresponding to type (II). We have confirmed that a copolymer corresponding to type (II) is obtained when hot-water soluble partially acetalized polyvinyl alcohol prepared by treating polyvinyl alcohol in solid form in a heterogeneous reaction system that employs a reaction bath containing an aldehyde and, preferably, an acid in accordance with this invention is used as the raw material from which the fiber products are spun.

The known art of preparing polyvinyl acetals, as previously mentioned, employs the so-called homogeneous reaction system wherein the aldehyde reacts with an aqueous polyvinyl alcohol solution. Statistically speaking, it-is assumed that, even if partially, acetalization is eflected to polyvinyl alcohol obtained from a homogeneous system, the product takes the form of a copolymer molecular model as'represented by (I).

The method of carrying out the reaction in a heterogeneous system in accordance with this invention does not cause any acetalization among the crystalline regions that exist in polyvinyl alcohol solids (pulverized polyvinyl alcohol). It is assumed that when acetalization is carried out to such an extent that polyvinyl alcohol is still soluble in hot water, the reaction mainly occurs in the amorphous regions. This can be readily shown by the follow- .ing experimental results. The reaction rate of acetalization of pulverized polyvinyl alcohol is plotted in Figure 1. V The. reaction is. carried out by adding .40 grams. of polyvinyl alcohol to a mixture of 37 grams of 37% formalin, 40 grams of sulfuric acid and 380 grams of water at a temperature of 40 C. As shown in Figure l, the reaction rate of acetalization of pulverized polyvinyl alcohol in a heterogeneous system can be divided into two difierent parts, one is that the reaction rate is very rapid and the other is that the rate is slow. It is assumed that the part wherein the reaction rate proceeds rapidly shows that reactions are taking place in the amorphous regions of polyvinyl alcohol particles, and the portion wherein a slow reaction rate is indicated is where reactions are taking place in the crystalline regions. Acetalization. carried out to such an extent that polyvinyl alf cohol particles still retain their solubility in hot water in accordance with the present invention, is restricted to reactions in the amorphous regions where the rate of reac tion proceeds rapidly. The degree of acetalizationde pends on the degree of heat-treatment to which polyvinyl alcohol has been subjected, the conditions of acetalization and the type of aldehyde employed.

When pulverized polyvinyl alcohol, which has been subjected to an acetalization reaction wherein the reaction occurs only in the amorphous regions and the crystallineregions are left unafiected, is heated in water until a molecular dispersion is obtained, the resultant copolymer is that corresponding to type (II) mentioned above. Fiber products obtained by spinning this solution do not lose their highcrystallizability and possess superior fiber properties.

In order to confirm the above observations, properties of fibers obtained by conventional methods from copolymers of type (I) (partially acetalized polyvinyl alcohol prepared by acetalization in a homogeneous system) and from copolymers of type (II) (partially acetalized polyvinyl alcohol prepared in accordance with the present invention) are tabulated in Table 2.

Softening point: Temperature at which the fibers become soft and are unable to be led on to the bars of a heated thread advancing roller (luring the heat-treatment process.

Softening point in water: Temperature at which the fibers shrink to one third of their original length when heated in water in a sealed tube.

It is seen that partially tacetalized polyvinyl alcohol fibers obtained by the homogeneous reaction system possess low softening points. High wet heat resistance cannot be imparted to such fibers even after the final heat-treatment and formalization. The results in Table 2 show that a copolymer corresponding to type (II) is obtained by partial acetalization of pulverized polyvinyl alcohol under heterogeneous reaction conditions, and that this method offers an advantage over the conventional reaction which comprises acetalizing polyvinyl alcohol under homogeneous reaction conditions. The above descriptions are based on experiments with pulverized polyvinyl alcohol, but the same effects are obtained with polyvinyl alcohol in fibrous, film or chip form.

Fibers that have been prepared from partially acetalized polyvinyl alcohol in accordance with the present invention and subjected to conventional aftertreatment processes show extremely good dry and wet heat resistance In addition such fibers exhibit very high elastic recovery at low strain. a

. Q 'It is well 'known that conventional polyvinyl alcohol synthetic fibers do not possess sufficient elastic recovery to render them applicable to practical uses. In order to overcome this disadvantage, numerous proposals have been suggested in the field of aftertreatment. One of the prevailing methods which was found to improve the elastic properties of polyvinyl alcohol fibers is to treat the fibers with such compounds as, butyraldehyde, nonylaldehyde, benzaldehyde, o-chloro benzaldehyde, naphthaldehyde, furfural, cyclohexyl aldehyde, etc. According to the present invention, it is possible to improve the elastic properties without resorting to such methods mentionediabove, as can be readily seen from Table 3.

Noie.(l) The degree of partial acetalization was held at 6%. (2) .Benzalization of untreated polyvinyl alcohol was carried out in the final attertrcatrnent stage.

One of the features of partial acetalization is that its contribution to elastic recovery depends on the degree of acetalization and is independent of the type of aldehydes oracetals employed.

Another feature is that when partial acetalization is carried outwith an aldehyde containing a basic group, a .fiber possessing increased level dyeing properties is obtained compared with the method wherein the same aldehyde is used to the fiber during the secondary acetaliza- .tion stage. This is attributed to the fact that the basic groups are more uniformly distributed among the fiber structure of the partially acetalized polyvinyl alcohol fiber. Whereas a degree of partial-acetalization preferably, from 3% to 5% is required to expect a definite improvement in the elastic properties of fibers subjected to a partial acetalization with aldehydes containing a basic group, a degree of partial acetalization from 0.4% to 0.8% is sufficient to achieve an improvement in dyeability.

The improvementsin elastic properties and dyeability obtained with fibers prepared from partially acetalized polyvinyl alcohol have been mentioned above. An .example of the mechanical properties are tabulated in Table 4.

Nte.-Thc degree.oilpartial.acetalization has been held at.

. When polyvinyl alcohol that has been partially acetalized in .solid form for .the purpose of spinning into fiber products is employed, untreated polyvinyl alcohol may be added to the spinning solution. In order to minimize the obstruction of crystallization during heattreatment, it is necessary to keep the unsaponified acetyl groups combined to the polyvinyl .alcohol to a degree of the orderof 0.2% or less. 1 p

The following specific examples are given for the purpose of promoting a better-understanding of the invenart ste geneous solution is obtained.

,tion of 5%.

i 1 l0 1 tion and 'it will, of course, be understood that they not tobe considered limitative.

Example 1 'and contains 0.5 mol percent of unsaponified acetyl groups. This is next heated in a kneader for 6 hours at C. and simultaneously pulverized to yield heat-treated polyvinyl alcohol powders of 10 mesh or more. The heat treated polyvinyl alcohol powders are treated for 3 hours at 40 C. in an aqueous solution (bath ratio: 10) consisting of 20 g./l. of sulphuric acid and 0.3 equivalent weight of formaldehyde to obtain partially formalized polyvinyl alcohol having a degree of formalization of 8%. After the reaction the product is washed repeatedly until the waste solution gives a pH of 6.5 to 7.5.

Partially formalized polyvinyl alcohol. thus obtained is placed in a kneader to which water is added to yield a 27% aqueous solution. This mixture is heated to C. and held at this temperature for 5 hours until a homo- During the dissolving process 0.05% (based on the Weight of the solution) ofa non-ionic active agent such as others of polyethylene glycol and stearyl alcohol is added to the above mixture. This solution has a viscosity of 225 poises at 80 C. and is extruded through a spinnerette having fifteen 0.09 mm. diameter holes by means of a gear pump, and formed into filaments by the dry spinning method. The spinning ma- .chine consists of a spinning cell 5 meters long and 20 centimeters in diameter provided with a spinnerette :at the top. Air, preheated to a temperature of .C., is fed through the lower part of the cell. 50 denier fila- .ments are wound at the bottom of the cell by means of a godet roller at a peripheral speed of 100 rn./min. The

moisture content in the filaments at this stage is 5 Stretching is carried out at C. and employing a draw ratio of 600%. Heat-treatment is carried out in air heated to 210 C. for 1 minute. The filaments are next treated in an aqueous solution containing 4% of formaldehyde, 20% of sulfuric acid and 20% of sodium sulfate .for 60 minutes at 60 C. The product thus obtained has a high wet heat resistance, producing a shrinkage of 3% when treated in boiling water for 30 minutes, and has a minimum softening point of 200 C. The dry strength of the fibers is 3.5 g./d., the dry elongation 17% and the dry knot strength 2.5 g./d. The elastic recovery at 2% strain is 85%. Furthermore the fibers hardly exhibit any discoloration, yielding a color value of 8% as measured by "J-IS Standards L1013-5.12.

Example 2 Polyvinyl alcohol obtained by saponification of polyvinyl acetate as described in Example 1 is thoroughly .washed 'with methanol to remove all traces. of alkali. A 30% aqueous spinning solution is then prepared and filaments are extruded by the dry spinning method as de .scribedin the preceding example. Heat-treatment is carried out for 10 minutes at 180 C. The heat-treated polyvinyl alcohol fibers thus obtained are treated in filament .form for 60 minutes at 40 C. in an aqueous solution containing 1% of formaldehyde, 7% of sulfuric acid and 25% of sodium sulphate, yielding fibrous partially formalized polyvinyl alcohol having a degree of formaliza- After thoroughly washing the fibrous partially formalized polyvinyl alcohol with water, a spinning solution is prepared from which filaments are extruded as nients are subjected to stretching, heat-treatment and alcohol upon a mercury surface.

11' secondary formalization as described in the same example. The product fibers have a dry strength of 3.5 g./d., dry elongation of 18%, and a dry knot strength of 2.4 g./d. With regard to wet heat resistance, a shrinkage of 2% is obtained when treated in boiling water for 30 minutes. A minimum softening point of 200 C. is obtained.

The elastic recovery at 2% strain is 85%. The color value of the fibers is 9%.

Example 3 Polyvinyl alcohol obtained by saponification of polyvinyl acetate as described is thoroughly washed with methanol. A film 0.05 millimeter thick is formed by pouring a 10% aqueous solution of the purified polyvinyl jected to a heat-treatment for 5 minutes in air heated to 205 C. It is then treated for 60 minutes at 40 C. in

an aqueous solution containing a mixture of 5% formaldehyde, sulfuric acid and 25% sodium sulfate. The product is a partially formalized polyvinyl alcohol film having a degree of formalization of 6%. After a thorough washing, fibers are formed from this partially formalized product employing the spinning, stretching, heat- .treatment and secondary formalization stages described in Example 1. The product fibers have dry strength of 3.7'g./d., and a dry elongation of 17%. With regard to .wet heat resistance, a shrinkage of 2% when treated in boiling water for 30 minutes is observed. A minimum softening point of 200 C. is obtained. The elastic recovery at 2% strain is 88%.

Example 4 Partially formalized polyvinyl alcohol in powder form obtained as described in Example 1 is used to prepare a spinning solution from which filaments are spun by the 'wet spinning method. The spinning method comprises extruding a 13% aqueous solution of partially formalized polyvinyl alcohol by means of a gear pump into a coagulation bath through a spinnerette with 1500 holes, each 0.08 millimeter in diameter. The coagulation bath consisting of an aqueous solution containing 410 g./1. of sodium sulfate, the pH of the solution being 4.0. The length of the bath is 120 centimeters. The temperature is held at 45 C. The two emerging from the coagulation bath has a total denier of 3,000 and is wound on a godet roller having a peripheral speed of 16 meters per minute. The filaments are stretched to three times their original length at 40 C., then washed with water to remove the salt of the coagulation bath. After drying the filaments are subjected to a heat-treatment for 5 minutes in air heated to 220 C. The product is then treated in an aqueous solution containing 4% formaldehyde, 20% sulfuric acid and 20% sodium sulfate for 30 minutes at 60 C. The fibers thus obtained exhibits a shrinkage of 4% when treated in boiling water for 30 minutes. The softening point is 200 C. The dry strength of the fiber is 3.0 g./d., dry elongation 23%, dry knot strength 2.2

g./d. and an 85% elastic recovery at 2% strain.

Example 5 Heat-treated polyvinyl alcohol in powder form obtained as described in Example 1 is agitated for 5 hours at 40 C. in a methanol-water mixture (1:1) (bath ratio: 10)

containing 50 g./l. of sulfuric acid and 0.05 equivalent weight of benzaldehyde. The reaction is carried out in a heterogeneous phase at all times with the result that partially benzalized polyvinyl alcohol having a degree of benzalization of 3.8% is obtained. This partially benzalized polyvinyl alcohol is used as the spinning material, and spinning stretching, heat treatment and formalization is carried out as described in Example 1. The fibers thus obtained exhibits a shrinkage of 1% when treated in boiling water for 30 minutes. The minimum softening point is 200 C. The dry strength of the fibers is 3.5

The film is next sub- 7 g./d., dry elongation 17%, and an 82% elastic recovery at 2% strain. Example 6 Heat-treated polyvinyl alcohol in powder form obtained as described in Example 1 is treated in a bath (bath ratio: 10) containing 2% amino-acetaldehyde dimethylacetal and 20% sulfuric acid for 15 hours at 40 C. The partially amino-acetalized polyvinyl alcohol has a degree of aminoacetalization of 3% and readily dissolves in hot water. This is repeatedly washed with water at 20 C. until the waste solution becomes neutral. This partially aminoacetalized polyvinyl alcohol is dissolved in water from which fibers are extruded, stretched, heattreated and formalized as described in Example 1. Such fibers exhibit a shrinkage of 4% when treated in boiling water for 30 minutes. The minimum softening point is 200 C. The dry strength of the fibers is 3.0 g./d., dry elongation 25% and dry knot strength 2.0 g./d. The elastic recovery at 2% strain is 85 These fibers exhaust of acid dyes such as Solar Violet SBN, Diacid Fast Red, Xylene Fast Blue P from a 2% solution (liquor ratio 1:40). The diffusion constant according to Hills formula is 6 10- cm./min. The color value of the fiber is 33%.

Example 7 Heat-treated polyvinyl alcohol in powder form obtained as described in Example 1 is treated in a reaction bath (bath ratio: 10) containing 2.0% dimethyl-amino acetaldehyde dimethyl acetal, 5% hydrochloric acid and 20% sodium sulphate for 10 hours at 60 C. The partially dimethyl-amino acetalized polyvinyl alcohol has a dimethyl-amino acetalization degree of 5%. Sodium sulfate is added to the reaction bath as a coagulation agent for polyvinyl alcohol in order to retain the polyvinyl alcohol in solid form at all times, since the rate of reaction of dimethyl-amino acetaldehyde dimethyl acetal is slower than that of amino acetaldehyde dimethyl acetal described in Example 6 so that a higher reaction temperature has to be adopted.

Fibers obtained from this material by subjecting itto the-spinning, stretching, heat-treatment and formalization stages as described in Example 1, exhibit a shrinkage of 5% when treated in boiling Water for 30 minutes. The softening point is 200 C. The fibers have a dry strength of 3.3 g./d., dry elongation of 18%, dry knot strength of 2.3 g./d., and an 85% elastic recovery at 2% strain. The dyeability of the fibers with acid dyes are exceptionally good and is similar to that shown in Example 7. Discoloration of the fibers appear during the heat-treatmen process, the color value is 28% Example 8 Heat-treated polyvinyl alcohol in powder form ob tained as described in Example 1 is treated in a reaction bath (bath ratio: 10) containing 0.2% B-dimethyl-amino butyraldehyde dimethyl acetal and 20% sulfuric acid for 5 hours at 40 C. The partially fi-dimethyl-amino butyracetalized polyvinyl alcohol has an acetalization degree of 0.7% and readily dissolves in hot water. Fibers obtained from this material in accordance with the process described in Example 1 exhibits a shrinkage of 2% when treated in boiling water for 30 minutes. The minimum softening point is 200 C. The dry strength of the fibers is 3.8 g./d., dry elongation 15% and dry knot strength 2.7 g./d. No particular improvement in the elastic recovery is achieved, the elasticity recovery at 2% strain being 70%. This is due to the low degree of B-dimethylamino butyracetalization. The dyeability of the fibers is exceptionally good, exhausting acidic dyes such as Solar Violet SBN, Diacid Fast Red, Xylene Fast Blue P, from a 2% solution (liquor ratio 1:40). The diffusion constant, according to Hills formula of 3X10- cm./min. Since the degree of acetalization is low, discoloration is observed, the color value being 20%.

. Tie

Example 9 A spinning solution is prepared from a 1:5 mixture of partially dimethyl-amino acetalized polyvinyl "alcohol obtained as described in Example 7 andpolyvinyl alcohol. Fibers are extruded from this solution and subsequently stretched, heat treated and formalized as described in Example 1. The fibers thus obtained have similar dryrand wet heat resistance and .dyeability as those obtained in Example 8. The dry strength is 3.5 g./d., dry elongation "17%, and color value 20%.

Example 10 *tojleave a solidcontent of 42% and employing this resin 1 as the material for spinning.

Example 11 (based on the weight of amino acetalized alcohol) of formamide is added to the spinning solution prepared from partially amino acetalized polyvinyl alcohol as described in Example 6 for the purpose of preventing discoloration of fibers during heat-treatment. The resulting fibers possess similar dry and wet heat resistance, dyeability, strength and elastic recovery same as those obtained in Example 6. The color value, however, is decreased to 18%.

When the color stabilization process of adding alkalies to the spinning solution or immersing the material in an aqueous solution of caustic soda as described in Example is applied concurrently, the color value is decreased to 13%.

Example 12 Polyvinyl alcohol used for mixing described in Example 9 is treated in the following manner. Heat-treated polyvinyl alcohol in powder form obtained as described in Example 1 is suspended in an aqueous solution (bath ratio: 10) containing 0.5 g./d., of caustic soda for one hour at 40 C. The treated polyvinyl alcohol thus obtained contains only 0.1 mol percent of unsaponified acetyl groups. This secondary saponified polyvinyl alcohol is mixed with dimethyl-amino acetalized polyvinyl alcohol in a ratio of 1 to 4. Fibers obtained from this mixture have dry and wet heat resistance, strength, elastic recovery and dyeability similar to those shown in Example 9.

Example 13 Partially formalized polyvinyl alcohol described in Example 1 is employed as the spinning material. The extruded fibers are subjected to the stretching and heattreatment as described in Example 1. Secondary acetalization is carried out by treating the fibers in an aqueous solution (bath ratio: 1,000) containing 0.3% benzaldehyde and 23% sulfuric acid for three hours at 60 C. The fibers thus obtained have a degree of benzalization of 28%, and exhibits a shrinkage of 5%. The minimum softening point is 200 C.

The fibers thus obtained have a dry strength of 2.9 g./d., a dry elongation of and a dry knot strength of 2.1 g./d., and an elastic recovery of 93% at 2% strain.

' Example 14 Partially amino acetalized polyvinyl alcohol described in Example 6 is employed as the spinning material. The

extruded fibers are subjected to stretching and heatr en ge? treatment as described in Example 1. Secondary acetalization is carried out in an aqueous solution (bath ratio:

1,000) containing 0.3% benzaldehyde, 0.3% formaldehyde and 22% sulfuric acid for four hours at 55 C. The fibers thus obtained yielded a 15% increase in Weight by this treatment. When these fibers are treated in boiling Water for 30 minutes, they show a shrinkage of 2%. 'The softeningpoint is 200 C. The fibers have a dry strength of 3.4 g./d., dry elongation of 19%, dry

knot strength of 2.2 g./d., and a elastic recovery at 2% strain.

The fibers exhibit exceptionally good dyeability,

particularly to acid dyes, and exhausts Xylene Fast Blue hol synthetic fiber products by spinning a polyvinyl alcohol solution, stretching the spun fibers, heat-treating and acetalizing, the preparation of a polyvinyl alcohol spinning solution which comprises primarily heat-treating polyvinyl alcohol in solid form to such an extent that polyvinyl alcohol becomes insoluble in cold water but soluble in hot water, reacting the heat-treated solid polyvinyl alcohol with a member selected from the group consisting of aldehyde and acetal thereof in a heterogeneous system to form partially acetalized polyvinyl alcohol which is still soluble in hot water, washing the polyvinyl alcohol with cold water and dissolving the polyvinyl alcohol in hot water.

2. Process for the manufacture of polyvinyl alcohol synthetic fiber products which comprises primarily heattreating polyvinyl alcohol in solid form to such an extent that polyvinyl alcohol becomes insoluble in cold Water but soluble in hot water, reacting the heat-treated solid polyvinyl alcohol with aldehyde selected from the group consisting of formaldehyde, acetaldehyde and benzaldehyde in the presence of an acid catalyst to form partially acetalized polyvinyl alcohol which is still soluble in hot water, washing the polyvinyl alcohol with cold water, dissolving the polyvinyl alcohol in hot water to prepare a spinning solution, spinning and streching the polyvinyl alcohol to form fibers, and secondary heat-treating and acetalizing the fibers.

3. Process for the manufacture of polyvinyl alcohol synthetic fiber products which comprises: primarily heattreating polyvinyl alcohol in solid form, to such an extent that polyvinyl alcohol becomes insoluble in cold Water but soluble in hot water, reacting the heat-treated polyvinyl alcohol with a member selected from the group consisting of aldehyde containing a basic group and acetal thereof in the presence of an acid catalyst in a heterogeneous system to form partially acetalized polyvinyl alcohol which is still soluble in hot water, washing the polyvinyl alcohol with cold water, dissolving the polyvinyl alcohol in hot Water to prepare a spinning solution, Spinning the solution to form fibers, secondary heattreating the fibers and treating the fibers with an aqueous henzaldehyde solution containing formaldehyde in the presence of an acid catalyst to acetalize the fibers.

4. Process according to claim 3 wherein starting polyvinyl alcohol to be primarily heat-treated contains not more that 0.2 mol percent of unsaponified acetyl groups.

5. Process for the manufacture of polyvinyl alcohol synthetic fiber products which comprises primarily heat treating polyvinyl alcohol in solid form to such an extent that polyvinyl alcohol becomes insoluble in cold water but soluble in hot water, reacting the heat-treated polyvinyl alcohol with a member selected from the group consisting of aldehyde containing an amino group and acetal thereof in the presence of an acid catalyst in heterogeneous system to form partially acetalized polyvinyl alcohol which is still soluble in hot water, washing the polyvinyl alcohol with cold water,-dissolving the 'polyvinyl alcohol after neutralization with alkali, in hot 'Water to prepare a spinning solution spinning the solution to form fibers, streching and secondary heat-treatacetaldehyde, dimethyl-amino acetaldehyde, diethylamino acetaldehyde, pyrrolidino acetaldehyde, phthalimido acetaldehyde, piperidino acetaldehyde, dimethylamino propionaldehyde, dimethyl-amino benzaldehyde,

dipropyl-amino acetaldehyde, dibutyl-arnino acetaldehyde, diethyl-amino propionaldehyde, dipropyl-amino propionaldehyde, dibenzyl-amino propionaldehyde, pipe'ridino propionaldehyde, dimethyl-amino butyraldehyde, diethyl-amino butyraldehyde, dipropyl-amino butyraldehyde, dibutyl-amino butyraldehyde, dibenzylamino butyraldehyde, piperidino-amino butyraldehyde, dimethyl-amino hydroxy butyraldehyde and their acetals.

7. Process according to claim wherein acid catalyst is hydrochloric acid.

18. Process according to claim 5 wherein neutralization with alkali is effected by adding a compound selected from the group consisting of sodium hydroxide, potassium hydroxide, sodium carbonate and sodium bicarbonate to the polyvinyl alcohol spinning solution.

9. Process according to claim 5 wherein neutralization is effected by immersing the washed solid polyvinyl alcohol in an aqueous solution of a compound selected from the group consisting of sodium hydroxide, potassium hydroxide, sodium carbonate and sodium bicarbonate.

10. Process for the manufacture of polyvinyl alcohol synthetic fiber products Which comprises primarily heattreatingpolyvinyl alcohol in solid form to such an extent that polyvinyl alcohol becomes insoluble in cold water but soluble in hot water, reacting the heat-treated polyvinyl alcohol with a member selected from the group consisting of aldehyde containing an amino group and acetal thereof in the presence of an acid catalyst in a heterogeneous system to form partially acetalized polyvinyl alcohol which is still soluble in hot water, washing the polyvinyl alcohol with cold Water, dissolving the added to the spinning solution.

solution, adding a compound selected the group consisting of urea, formamide, formic acid, ammonium formate formaldehyde, and dicyano diamide to the spinning solution, spinning the 'solution' .to form fibers, stretching and secondary heat-treating-the fibersand treating the fibers with an aqueous benzaldehyde solution containing formaldehyde in the presence of an acid catalyst. V

1 11. Process according to claim 10 wherein alkali-is 12. Process according to claim 1 wherein unreacted polyvinyl alcohol containing not more than 0 .2 mol percent of unsaponified acetyl group is added to the spinning solution.

13. Process for the manufacture of polyvinyl alcohol synthetic fiber products which comprises primarily'heattreating 'polyvinylalcohol in the form of powder to such an extent that polyvinyl-alcohol becomes insoluble in cold water but soluble in hot water, reacting the :heattreated polyvinyl alcohol with a compound selected from the groups consisting of aldehyde containing an amino group and acetal thereof in the presence of hydrochloric acid to form partially acetalized polyvinyl alcohol which is still soluble in hot Water,washing "the polyvinyl alcohol with cold water, immersing the washed alcohol in an aqueous alkaline solution, dissolving the polyvinyl alcohol together with unreacted polyvinyl alcohol having not more than 0.2 mol percent of unsaponified acetyl groups and urea in hot water to prepare a spinning solution, dry spinning the solution to 'form fibers, stretching and secondary heat-treating the 2,413,789 Scheiderbauer Ian. 7, 1947 2,610,360 Cline et a1. Sept. 16, 1952 VFOREIGN PATENTS 732,934 Great Britain June 29, 1955 OTHER REFERENCES Jones, 1.: Polyvinyl Alcohol, Part II, British Plaspolyvinyl alcohol in hot water to prepare a spinning tics, February 1944, pp. 77-83. 

1. IN A PROCESS FOR THE MANUFACTURE OF POLYVINYL ALCOHOL SYNTHETIC FIBER PRODUCTS BY SPINNING A POLYVINYL ALCOHOL SOLUTION, STRETCHING THE SPUN FIBERS, HEAT-TREATING AND ACETALIZING, THE PREPARATION OF A POLYVINYL ALCOHOL SPINNING SOLUTION WHICH COMPRISES PRIMARILY HEAT-TREATING POLYVINYL ALCOHOL IN SOLID FORM TO SUCH AN EXTENT THAT POLYVINYL ALCOHOL BECOMES INSOLUBLE IN COLD WATER BUT SOLUBLE IN HOT WATER, REACTING THE HEAT-TREATED SOLID POLYVINYL ALCOHOL WITH A MEMBER SELECTED FROM THE GROUP CONSISTING OF ALDEHYDE AND ACETAL THEREOF IN A HETEROGENOUS SYSTEM TO FORM PARTIALLY ACETALIZED POLYVINYL ALCOHOL WHICH IS STILL SOLUBLE IN HOT WATER, WASHING THE POLYVINYL ALCOHOL WITH COLD WATER AND DISSOLVING THE POLYVINYL ACOHOL IN HOT WATER . 